1. Field of the Invention
The present invention relates generally to ink-jet printing and, more specifically to a method and apparatus for dynamic print mode adjustment.
2. Description of Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992) Vol. 43, No. 6 (December 1992) and Vol. 45, No.1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy [sic] Devices, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).
FIG. 1 (PRIOR ART) depicts an ink-jet hard copy apparatus, in this exemplary embodiment a computer peripheral printer 101. For convenience in describing the art and the present invention, all types of ink-jet hard copy apparatus are sometimes hereinafter referred to as “printers;” all types, sizes, and compositions of print media are also referred to as “paper;” all compositions of colorants are sometimes referred to as “ink;” and all embodiments of an ink-jet writing instruments are simply referred to as a “pen;” no limitation on the scope of the invention is intended nor should any be implied.
A housing 103 encloses the electrical and mechanical operating mechanisms of the printer 101. Operation is administrated by an electronic controller (usually a microprocessor or application specific integrated circuit (“ASIC”) controlled printed circuit board) 102 connected by appropriate cabling to a computer (not shown). It is well known to program and execute imaging, printing, print media handling, control functions and logic with firmware or software instructions for conventional or general purpose microprocessors or with ASIC's. Cut-sheet print media 105, loaded by the end-user onto an input tray 120, is fed by a suitable paper-path transport mechanism (not shown) to an internal printing station, or “print zone,” 107 where graphical images or alphanumeric text are rendered onto adjacently positioned paper. A carriage 109, mounted on a slider 111, scans the print zone 107 (stationary paper wide ink-jet writing instruments are also known in the art and may be employed with the present invention). An encoder 113 subsystem is provided for keeping track of the position of the carriage 109 at any given time. A set of individual ink-jet pens, or print cartridges, 115X are mounted in the carriage 109. Reusable printhead systems are fluidically coupled by tubing 119 to replaceable or refillable ink reservoirs 117X (generally, in a full color system, inks for the subtractive primary colors, cyan (X=C), yellow (X=Y), magenta (M) and true black (X=K) are provided; ink fixer (X=F) solutions are also sometimes provided). Once a printed page is completed, the print medium is ejected onto an output tray 121. As indicated by the labeled arrows, the scanning axis is referred to as the “x-axis,” the paper transport path as the “y-axis,” and the printhead firing direction as the “z-axis.”
In essence, the ink-jet printing process involves digitized dot-matrix manipulation of drops of ink ejected from a pen onto an adjacent sheet of paper. One or more ink-jet type writing instruments includes a “printhead,” consisting generally of drop generator mechanisms and a number of columns of ink drop firing nozzles. Each column, or color-defined, selected subset of nozzles (referred to in the art as a “primitive”), selectively fires ink droplets (typically each being only a few picoliters in liquid volume) that are used to create a predetermined print matrix of dots on the adjacently positioned paper as the pen is scanned across the media. A given nozzle of the printhead is used to address a given matrix column print position on the paper (referred to as a picture element, or “pixel”). Horizontal positions, matrix pixel rows, on the paper are addressed by repeatedly firing a given nozzle at matrix row print positions as the pen is scanned. Thus, a single sweep scan of the pen across the paper can print a swath of tens of thousands of dots. The paper is stepped to permit a series of contiguous swaths. Complex digital dot matrix manipulation is used to form alphanumeric characters, graphical images, and even photographic reproductions from the ink drops. Stationary, page-wide, ink-jet printheads are also contemplated and are adaptable to the present invention.
The computerized printing processes employed with dot matrix manipulation are often referred to simply as “print modes.” Print modes and resultant printer operations are generally chosen and fixed for any given setting of print media selection and print quality (e.g., an end-user computer application selection of “special media” and “photo quality,” or the like as would be known in the art). Assignee's pending patent application, U.S. Ser. No. 09/181951, by J. M. Brenner et al., discloses changes to printer behavior based on what the user has done.
As a writing system degrades over its product life, whether from age or use, print quality can also degenerate. Based on product life, a fixed, predetermined, print mode is chosen during development of a product for each media/print quality setting available to the end user. Usually each print mode is set based on a worst case operational scenario (maximum mechanical tolerance variations, pen variations, media variations, and the like parameters as would be known to those skilled in the art). By using a worst case scenario, print quality does not fall below an acceptable predetermined level based on empirical product development data. One-pass per print swath, bidirectional printing, is the fastest scanning type print mode. However, it is very sensitive to missing or misdirected nozzles, paper skew, and the like. A common solution is to use slower print modes to improve print quality (e.g., multi-pass swath printing and the like). Thus, throughput is slower than competing products such as laser printers.
Some exemplary print defects and customary causes are:
Operation AttributePrint DefectNOZZLE(S) OUTStreakingLINE FEED ADVANCE ERRORSLight/dark linesMISDIRECTED NOZZLESLight/dark linesWEAK NOZZLESStreakingPRINTHEAD MISALIGNMENTSStaggered lines and granularityTHETA-Z (PRINTHEAD SKEW)Staggered lines and bandingDROP WEIGHT VARIATIONOverall dark/light variations,insufficient saturation,or ink bleed throughDOT SHAPE/SIZE VARIATIONDark/light regions, fuzzy lines
FIG. 4 is TABLE 1, providing more complete listing of Operational Attributes and related Print Defects; the foregoing list of eight of these Attribute/Defect pairs will be used as an exemplary set for describing the present invention.
A variety of means for recognizing such print defects are known in the art. For example, Lesniak in U.S. Pat. No. 5,387,976 discloses a METHOD AND SYSTEM FOR MEASURING DROP-VOLUME IN INK-JET PRINTERS, issued Feb. 7, 1995; optical sensing techniques and the use of test patterns have long be used, such as a MONITORING AND CONTROLLING QUALITY OF PEN MARKINGS ON PLOTTING MEDIA, U.S. Pat. No. 5,262,797 filed by Boeller et al. on Apr. 4, 1990 (each assigned to the common assignee herein and incorporated herein by reference).
An ink-jet printer including the present invention would employ one or more of such defect detection subsystems in order to obtain real-time information regarding current printing conditions. While familiarity with such means is helpful, it is not essential to an understanding of the present invention.
Generally, however, a printer is capable of much higher performance assuming optimum operational conditions. Thus, some of this degradation may be compensated if the writing system can self-determine the actual cause of the degradation. Therefore, there is a need for print mode control based upon real-time feedback regarding status of various components within the ink-jet writing system.